1. Field of the Invention
The present invention relates to a lens film possessing excellent antistatic properties, and more particularly to a lens film suitable for displays of word processors, computers, televisions and other applications by virtue of an antifouling property of the surface thereof against dust and freedom from uneven adhesion at the time of lamination, and a surface light source and a liquid crystal display device using the same.
2. Background Art
Lens films incorporated as a component into displays for electronic equipment, such as personal computers and word processors, and other various commercial displays have a lens layer comprising a substrate film one side of which has been embossed, or comprising a shaped and cured thermoplastic resin or ultraviolet-cured resin provided on a transparent substrate film. In use, these lens films have been incorporated into liquid crystal display devices and the like.
When the lens film is used together with a surface light source device for assembling, a protective film covering the lens film should be separated and removed. This has involved a problem that static electricity is created at the time of separation of the protective film, which is causative of the deposition of foreign materials onto the surface light source device.
Further, in many cases, two lens films are used in such a manner that the prismatic ridge line of one of the lens films is orthogonal to the prismatic ridge line of the other lens film. At that time, the prismatic surface of the lower lens film and the flat surface of the substrate of the upper lens film are partially adhered to each other due to the influence of static electricity, and, even after the incorporation of the assembly into a liquid crystal display device, uneven adhesion unfavorably creates display of an image having unacceptable poor quality.
In order to prevent the creation of static electricity, an attempt has been made to coat the surface of a concave or convex lens with an antistatic agent to provide an antistatic layer as shown in FIG. 8. Evenly providing the antistatic layer is highly difficult from a technical viewpoint. In this case, the appearance of the lens film and the image in the liquid crystal display device become uneven, posing problems such as remarkably deteriorated optical properties and separation of the antistatic layer.
A method for the formation of a conductive thin layer by the deposition of a metal or the like has also been disclosed. However, evenly providing a metal deposit onto a concave or convex lens is difficult, disadvantageously leading to a variation in optical properties and a high cost.
An object of the present invention is to provide a lens film free from the above problems of the prior art.
The above object can be attained by a lens film of the present invention provided with specific antistatic means.
According to one aspect of the present invention, there is provided a lens film comprising: a transparent substrate film; and a lens layer of a concave lens or a convex lens provided on at least one side of the substrate film, wherein the lens layer comprises a resin composition with conductive fine particles dispersed therein and has a surface resistivity of not more than 1012 xcexa9/xe2x96xa1.
According to another aspect of the present invention, there is provided a lens film comprising: a transparent substrate film; a conductive layer provided on at least one side of the substrate film; and a lens layer of a concave lens or a convex lens provided on the conductive layer, the conducive layer having a surface resistivity of not more than 1012 xcexa9/xe2x96xa1.
Further, the present invention provides a surface light source comprising the above lens film, the lens film in its light-receiving side being disposed on the light-outlet side.
Furthermore, the present invention provides a liquid crystal display device comprising the above surface light source.
The lens film of the present invention provided with the above specific antistatic means can effectively prevent the generation of static electricity. Therefore, even immediately after the removal of the protective film in the lens film, the amount of electrification is small. Further, problems involved in assembling of a surface light source device attributable to static electricity can be solved such as deposition of foreign materials due to static electricity generated at the time of separation of a protective film from the lens film and uneven adhesion observed in use of two lens films in such a manner that the prismatic ridge line of one of the lens films is orthogonal to the prismatic ridge line of the other lens film.